Environmental determinants have been implicated in substance abuse behaviors, levels of addiction, risk of overdose, risky behaviors, and overall mental and physical health. An emerging understanding of the contribution of neighborhood environment to health and substance abuse behaviors has created a unique opportunity to develop an innovative randomized trial of a place-based prevention strategy. This study focuses on the stabilization of abandoned, vacant lots as a potential prevention strategy for public substance abuse. A preliminary study by the research team showed that the vacant lot stabilization program reduced crime and enhanced select health outcomes. The stabilization of vacant lots is important because they are in great abundance, singled out by community members as important, and are highly modifiable, community-level factors with potential for sustained, long-term health and safety benefits at relatively little cost. In 1999, the Pennsylvania Horticultural Society began a program to stabilize and maintain vacant lots in key Philadelphia neighborhoods. This program involves cleaning and greening abandoned vacant lots by removing debris, grading the land, planting grass and trees to create a park-like setting, and installing low fences around its perimeter to show that the lot is cared for and to deter illegal dumping. This study will test the impact of such a program on public substance use and related behaviors. The random assignment of 420 vacant lots stratified in four geographic sections of Philadelphia will be done in three trial arms: vacant lot stabilization (full treatment), trash clean-up only (trash control), and no vacant lot stabilization or clean-up (no treatment). Substance abuse and related health and safety outcomes on or near the lots will be measured in the years before and after treatment. Through this we intend to accomplish the following proposed specific aims: (1) To determine if the stabilization of randomly chosen vacant lots changes the public occurrence of illegal drug trafficking and consumption compared with vacant lots that have been randomly chosen to receive only trash clean-up and lots that have been randomly chosen to receive nothing; (2) To determine if the stabilization of randomly chosen vacant lots changes the public occurrence of illegal drunkenness and drinking compared with vacant lots that have been randomly chosen to receive only trash clean-up and lots that have been randomly chosen to receive nothing; (3) To determine incremental cost-effectiveness estimates of vacant lot stabilization in terms of the cost of vacant lot stabilization per instances of illegal drug trafficking and consumption and illegal public drunkenness and drinking avoided.